sched/preempt: Add static_key() to preempt_notifiers
Avoid touching the curr->preempt_notifier cacheline when not needed.
Provides a small improvement on pipe-bench:
taskset 01 perf stat --repeat 10 -- perf bench sched pipe
before:
Performance counter stats for 'perf bench sched pipe' (10 runs):
12385.016204 task-clock (msec) # 1.001 CPUs utilized ( +- 0.34% )
2,000,023 context-switches # 0.161 M/sec ( +- 0.00% )
0 cpu-migrations # 0.000 K/sec
175 page-faults # 0.014 K/sec ( +- 0.26% )
41,376,162,250 cycles # 3.341 GHz ( +- 0.11% )
17,389,139,321 stalled-cycles-frontend # 42.03% frontend cycles idle ( +- 0.25% )
<not supported> stalled-cycles-backend
68,788,588,003 instructions # 1.66 insns per cycle
# 0.25 stalled cycles per insn ( +- 0.02% )
13,449,387,620 branches # 1085.940 M/sec ( +- 0.02% )
20,880,690 branch-misses # 0.16% of all branches ( +- 0.98% )
12.372646094 seconds time elapsed ( +- 0.34% )
after:
Performance counter stats for 'perf bench sched pipe' (10 runs):
12180.936528 task-clock (msec) # 1.001 CPUs utilized ( +- 0.33% )
2,000,077 context-switches # 0.164 M/sec ( +- 0.00% )
0 cpu-migrations # 0.000 K/sec
174 page-faults # 0.014 K/sec ( +- 0.27% )
40,691,545,577 cycles # 3.341 GHz ( +- 0.06% )
16,446,333,371 stalled-cycles-frontend # 40.42% frontend cycles idle ( +- 0.18% )
<not supported> stalled-cycles-backend
68,570,100,387 instructions # 1.69 insns per cycle
# 0.24 stalled cycles per insn ( +- 0.01% )
13,389,740,014 branches # 1099.237 M/sec ( +- 0.01% )
20,175,440 branch-misses # 0.15% of all branches ( +- 0.52% )
12.169253010 seconds time elapsed ( +- 0.33% )
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
1cde2930e1